Test for CSV API shortcut

Adding support for delivering a list of IDs to issue summary and patches
included in CSV format from where they will be parsed and converted to
markup format. This makes integration to automation tools a bit easier.
Added CSV shortcut API for two fields

Since issue summary and patches included fields are often filled with a
list of IDs only, added a CSVish shortcut method with which API user
does not need to convert to markup format by himself, but just deliver a
comma separated list of IDs.
Test for default prefix for CSV shortcut API parameters

Going to add support for defining default prefixes for the two CSV
shortcut API parameters. The default is separate from the default in
external services config because often issues come from one service and
patches from another.
Implemented CSV API shortcut parameters

Added API parameters issue_summary_csv and patches_included_csv that
take a comma separated list of IDs, prepend the ones without a prefix
with a default prefix if defined, and converts to markup list format.

So, sending issue_summary_csv="1234,2345,5762" will turn to
* [[1234]]
* [[2345]]
* [[5762]]

or, if a default prefix is defined, to
* [[BZ#1234]]
* [[BZ#2345]]
* [[BZ#5762]]